1. Field of the Invention
This invention relates to tape drive data storage systems. More particularly, the invention is directed to the control of tape tension during tape drive operation to facilitate data read/write accuracy.
2. Description of the Prior Art
By way of background, during operation in a tape drive data storage apparatus, a tape medium is transferred from a supply reel to a take-up reel while data is read from or written to tape by one or more read/write heads. Typically, the tape medium and the supply and take-up reels are mounted inside a tape cartridge that is inserted into a slot in the tape drive so that the tape is in magnetic contact with the read/write heads. The tape is advanced past the read/write head(s) by means of a pair of motors, one for each reel, which drive the reels at a desired tape speed. The motor that drives the supply reel is sometimes called the trailing motor and the motor that drives the take-up reel is sometimes called the advance motor. Motion of the trailing motor is controlled relative to motion of the advance motor to provide the necessary tape tension for desired positioning between the tape and the read/write head(s). It is desirable to maintain constant tape tension for optimum performance of data transfer through the read/write head(s). Improper tape tension can lead to unreliable positioning of the tape relative to the read/write head(s), which can produce low readback signal amplitude and poor data transfer reliability, and causes poor stacking on the reels which can result in damaged media and therefore data loss.
In light of the foregoing, all modern tape drive data storage devices implement some form of tape tension control. Available options include tension transducers, estimation of the amount of tape on the reels, pack radius monitoring devices or pack radius estimating, tachometers, friction capstans and closed loop monitoring of motor current. These options can be insufficient in providing precise tension control and may require additional hardware in the tape path that can negatively contribute to high performance tape path requirements.
Other tape tensioning options include data readback signal monitoring and tape tension control as a function of data rate or signal level. A still further option includes monitoring of test signals recorded in a scratch area of the tape. These options are also undesirable because they require added hardware or additional write/read sequences for their implementation.
Accordingly, it is desired to have an improved method of adjusting tape tension in a tape drive data storage system.